From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Comparison of engine bearing and lubrication schemes for the Kestrel, Merlin, and Bentley models.
| Identifier | ExFiles\Box 115\2\ scan0574 | |
| Date | 22th July 1940 | |
| Cont'd.{John DeLooze - Company Secretary} - 2 - Rm{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden}I/ML.22.7.40 Furthermore, the Kestrel scheme resembled the successful scheme finally used on the 4¼ litre Bentley. The Kestrel scheme was apparently successful and the Merlin is not. The difference between successful and unsuccessful schemes would appear from this to be due to the pressure or not of grooves in the bearing and holes in the journal. It is appreciated that holes and grooves were used on the Kestrel centre main bearing because it had to feed a big end bearing and that no big end is fed from the Merlin centre main bearing. The fact does remain, however, that the one scheme is successful and the other is not. Presumably the object of the Merlin scheme is to keep the effective bearing surface of the centre bearing as large as possible, since for design reasons the overall length of each bearing is practically the same. The loading for the centre bearing is about double that for the end bearings under all conditions, and 25% greater than for the intermediates, under T.V. conditions. A complete annular groove 7/16" wide would increase the loading 16% i.e. maximum load due to inertia only at 3,600 r.p.m. would increase from 2,950 lb/ins. to 3,420 lb/ins. A 190 degree (included angle) groove, as on Kestrel, would increase it's 7½% and an 80% groove, as proposed by By, would mean an increase of only 3% Since the mathematics of narrow plain bearing lubrication is very uncertain, it cannot accurately be stated what happens to the oil film, but from previous practice it would seem that whilst it may increase the bearing loading, a part annular groove more than compensates for this by maintaining the oil film intact under heavy bearing loads. A factor has been evolved for comparing the lubrication system capabilities of the Merlin and the Bentley 60. It is thought that this factor is directly proportional to the oil pump delivery, and indirectly proportional to the maximum loading on the bearing and the leakage path at the bearings. The leakage path is assumed to be the total bearing perimeter for all bearings using main oil pressure. Strictly speaking, the lengths of the bearings and the clearances should be taken into account, but both produce mathematically uncertain effects and are therefore ignored. - Continued - | ||